As the population grows older and older, the deterioration of visual functions becomes more and more apparent and serious. There are numerous eye diseases which are closely related to aging, such as glaucoma, age-related macular degeneration (AMD), optic neuropathy, ischemic retinopathy, senile cataract, and the like. These eye diseases are the major ones which cause visual disturbance or even blindness of the elderly.
The retinal pigment epithelium (RPE) is composed of monolayer of cells and located between the retinal photoreceptors and the choroidal blood vessels which plays a key role in the mechanical and metabolic support of the photoreceptors. In addition, dysfunctioned RPE is the main cause of some ocular diseases, such as proliferative vitreoretinopathy (PVR), uveitis and AMD. AMD and other diseases, such as diabetic retinopathy (DR), are probably linked to the effects of oxygen radicals derived from light or metabolic reactions.
On the other hand, ocular blood flow is also closely related to numerous eye diseases, including glaucoma, ischemic retinopathy, and age-related macular degeneration (AMD). Thus, maintenance of normal ocular blood flow is essential to prevent/treat the aforementioned eye diseases.
Age-related macular degeneration (AMD) is the leading cause of blindness in people over the age of 65 in the United States and Western Europe. Risk factors common to both continents include increasing age, cigarette smoking, hypertension, angina and a positive family history. AMD exists in both non-exudative and exudative forms. The non-exudative form involves atrophy of the central retina with a slow and progressive loss of central vision. The exudative form is characterized by the growth of new blood vessels through Bruch's membrane into the subretinal space, and the development of choroidal neovascularization (CNV) through an angiogenic process. Angiogenesis is often triggered by ischemia and hypoxia. As the macula has only a single blood supply, and the retina has the highest uptake of oxygen in the body, it is not surprising to observe that ischemia is strongly associated with AMD development (Strauss O., Physiol. Res. 200; 85(3):845-881).
Since the epithelium is very vulnerable to changes in oxygen tensions and oxygen radical-linked stress, reactive oxygen species (ROS) produced in the RPE during ischemia-linked diseases may be injurious to RPE cells. An important “early” event of AMD is the loss of RPE cells due to oxidative damage. Oxidative stress has been recognized to be involved in the etiology of several age-related chronic diseases, such as cancer, diabetes, neurodegenerative and cardiovascular diseases.
Propolis is a resinous mixture that honeybees collect from tree buds, fruits, sap flows, or other botanical sources. Propolis from different areas may contain different active components. It has been reported to possess various active components and exhibit a broad spectrum of biological activities, including antitumor (Ahn et al., Cancer Lett. 2007, 252: 235-243.), antioxidant (Altu{hacek over (g)} et al., Brain Res. 2008 Mar. 27; 1201: 135-42.), antibacterial (Drago et al., J Appl Microbiol. 2007, 103: 1914-1921.), antiviral (Shimizu et al., Antivir Chem Chemother. 2008, 19: 7-13.), antifungal (Silici et al., J Pharmacol Sci. 2005, 99: 39-44.), and anti-inflammatory activities (Grunberger et al., Experientia 1988, 44: 230-232.). However, to the applicant's knowledge, there is no report on that any active component of propolis can be used to treat ocular diseases, maybe except cancer in the eyes as suggested by the antitumor activity known in the art.